Summary: We consider the Kolmogorov equation associated with the stochastic Navier-Stokes equations in 3D and prove existence of a solution in the strict or mild sense. The method consists in finding several estimates for the solutions \(u_{m}\) of the Galerkin approximations of \(u\) and their derivatives. These estimates are obtained with the help of an auxiliary Kolmogorov equation with a very irregular negative potential. Although uniqueness is not proved, we are able to construct a transition semigroup for the 3D Navier-Stokes equations. Furthermore, this transition semigroup has a unique invariant measure, which is ergodic and strongly mixing.